Mammalian central neurons have been grown in tissue culture to study 1) immunohistochemically identified peptidergic and GABAergic neurons, 2) opioid peptide synthesis by some of these neurons, and 3) the biochemical characteristics of specific receptors endogenous ligands. Sensory and spinal neurons stain specifically for nerve-specific enolase, while non-neuronal cultured cells do not. Some of the cultured neurons stain positively for either methionine or leucine-enkephalin, dynorphin substance P, somatostatin or glutamic acid decarboxylose (GAD). Enkephalinergic neurons can synthesize and release methionine-enkephalin when incubated with labelled methionine. Binding studies have demonstrated the existence of several types of receptor on cultured neurons including those for GABA, opioid peptides and benzodiazepines. The results show the utility of using cultured nerve and muscle cells as model systems to study, with neurochemical techniques, the synthesis of endogenous substances and the biochemical characteristics of their receptors.